Microwave plasmas are useful for processing various materials, such as chemical processing of gases or materials deposition systems. These systems can benefit from either high pressures or vacuum in a processing chamber, and typically contain dielectric windows through which the microwave power is provided to the processing chamber.
For example, industrial chemical processing of gases using microwaves can be accomplished by flowing the gases to be reacted through an elongated vessel while microwave energy is coupled into the vessel to generate a plasma. The plasma cracks the gas molecules into component species, such as the conversion of methane into hydrogen and carbon particulates, or the conversion of carbon dioxide into oxygen and carbon. Typical systems for microwave processing (e.g., chemical gas processing) include a quartz reaction chamber through which process materials flow, and a microwave magnetron source coupled to the reaction chamber through a waveguide. Systems are designed to control the effective coupling of the microwave energy into the reaction chamber, and the gas flow within the reaction chamber to improve the energy absorption by the flowing gas.
For the above reasons, microwave plasma reactors typically include a pressure barrier between a higher pressure and a lower pressure region of the reactor, that serves as a window through which microwave energy can penetrate and be used to create a plasma for processing of materials in the reactor. Pressure barriers also generally serve as a mechanical safety barrier to prevent a plasma created in a processing chamber from backflowing into the microwave energy source.